Low pressure gas distribution systems are prone to collecting liquids through condensation and inward liquid seepage. Aged distribution systems presently in use in many municipalities are often cast iron or steel and further prone to collecting dust and rust scale, particularly when flow direction is reversed. These conditions pose serious operational problems for utilities. Such problems often occur during the coldest time of year when throughput is maximized and weather condition make servicing difficult.
Polychlorinated biphenyl (PCB), presently classified as a hazardous material, has been used as a lubricant in compressors employed to boost gas pressure in the long transmission lines which deliver natural gas to utilities for local distribution. Even slight leakage of this compressor lubricant into the transmission lines can, over a prolonged period, result in the accumulation of pockets of the material at low points in the gas transmission system, presenting a potential source of further contamination of distribution systems supplied by the long transmission lines.
Consequently, an environmentally responsible utility must consider that all liquid waste material removed from its gas service lines is PCB contaminated and strictly adhere to all regulations mandated for the safe disposal of hazardous materials. Such compliance usually proves quite costly.
Heretofore it has been common practice to use "off-the-shelf" portable canister type electric vacuum machines equipped with high-efficiency particulate air (HEPA) filters on the exhaust outlets thereof to clear clogged gas mains and services. However, where a portable machine of the aforedescribed type is used it is generally necessary to rely upon the customer's electric service to power the machine. This practice has been an occasional source of customer dissatisfaction. The available customer power source, usually 110 v, imposes a further limitation upon the capacity of the machine which may be employed. As a result, a machine which can be used may lack the power to effectively clear a service of dust, rust scale, oils and water while operating in an environmentally responsible manner. The present invention is concerned with aforedescribed general problems.
Accordingly, it is the general aim of the present invention to provide a mobile self-powered, independently operable vacuum system which has sufficient power to clear gas lines of dust, rust scale, oils and water in an effective and environmentally responsible manner and which may also be employed to perform other incidental cleaning operation associated with a gas distribution system, as, for example, clearing distribution system valve boxes. It is a further aim of the present invention to provide an improved method for performing clearing operations on gas distribution systems in an environmentally responsible manner while substantially reducing hazardous waste material disposal cost.